Unlike other arrangements, if we dont get this right, business stops. There will be no trade. If we cant arrive at safeguards and other principles that allow compliance [with international nuclear standards] to be demonstrated, no nuclear trade will be able to continue.

Asked by the chair of the Commons business, energy and industrial strategy select committee if that would see reactors switching off, he said: Ultimately, when their fuels runs out, yes. Cowen said that in his view there was no legal requirement for the UK to leave Euratom because of Brexit: Its a political issue, not a legal issue.

The UK nuclear industry would be crippled if new nuclear cooperation deals are not agreed within two years, a former government adviser told the committee.

There is a plethora of international agreements that would have to be struck that almost mirror those in place with Euratom, before we moved not just material but intellectual property, services, anything in the nuclear sector. We would be crippled without other things in place, said Dame Sue Ion, chair of the Nuclear Innovation and Research Advisory Board, which was established by the government in 2013.

She said movement of the industrys best intellectual talent was made easier by the UKs membership of Euratom.

The government said it was working on alternative arrangements to Euratom. Describing the notification of withdrawal as a regrettable necessity when article 50 is triggered, energy minister Jesse Norman said that the UK saw clear routes outside of Euratom to address issues such as the trade of nuclear materials.

We take this extremely seriously and are devoting serious resources [to looking at new arrangements], he told the Lords science and technology committee on Tuesday.

Tom Greatrex, chief executive of the Nuclear Industry Association, said there was a lot to be done to put in place transitional measures replacing Euratom.

What were collectively warning about is the potential for there to be a very hard two-year period during which there are lots of other things the government has to deal with, that could leave it in a position where some of these things arent in place, he said. Greatrex said one possible option was an associate membership of Euratom.

Over the weekend, the GMB union called on ministers to reconsider their foolhardy rush to leave the treaty, claiming it could endanger the UKs entire nuclear future.

But the Office for Nuclear Regulation argued there could even be be some positives to leaving Euratom, such as a reduction in bureaucracy. If we relinquish Euratom there would be reduced burden from not having to comply with directives, said David Senior, an ONR executive.

Train operator hopes new facilities at its Gare du Nord terminal will stop ticket sales falling off a post-Brexit cliff

High up in the 19th-century edifice that forms the front of the Gare du Nord in Paris, Eurostar has found a new, grand perch.

The cross-Channel train service has a startling upgrade in store for its business travellers, the latest gambit to bolster a company that is right in the frontline of Brexit. Last week it unveiled a lounge designed to feel more like an elegant Parisian flat, all high ceilings and marble fireplaces, sofas and wide tables. A kitchen stocked with a buffet curated by the Anglo-French chef Raymond Blanc is also promised later this year.

Beyond lies a cocktail room, whose centrepiece is a sunken circular bar. It will serve an Anglique, which, Blanc advises, is the only drink that actually wards off a crise de foie and aids digestion. And of course there are plenty of places to work, if you get that far.

Investment at Eurostar is pressing ahead, even if the rail operator could be forgiven for feeling uneasy about running trains on the one fixed link between Britain and Europe.

The referendum came in an already difficult year for Eurostar, with bookings dropping away after terrorist attacks in Paris and Brussels. Strikes in the summer and the axing of 80 jobs followed: the company said that Junes vote had created uncertainty, and its ticket sales dipped again. What chance, then, with actual Brexit?

Eurostars chief executive, Nicolas Petrovic, is smoothly upbeat: Im an optimist. 1bn has been spent over the past three years, mostly on a fleet of new trains, more than half of which are now in service. Brexit or no Brexit, the traffic is only going to grow, he says. The economies of London, Paris and Brussels are more integrated than they have ever been.

However, Petrovic has said in the past that he sees no upside to Brexit. Eurostar, 55% owned by the French national rail operator SNCF, says it benefited greatly from the EU establishing common standards for aspects of its business, from train operation to employment. Possible headaches lie ahead in recruiting and retaining its diverse, international staff.

Analysts are uncertain about the effects of Brexit. Gerald Khoo, of stockbroker Liberum Capital, says there could be upsides and downsides: Fewer MEPs and civil servants going to Brussels but if UK companies really do pivot towards Paris, that could also be a boost.

Nicolas Petrovic with one of Eurostars new trains. Photograph: Martin Godwin for the Observer

A weak pound cuts both ways for a cross-border business, but Eurostars leisure travellers are still mostly Brits, who will need to shell out more.

Indeed, concerns exist in the minds of travellers. One Eurostar passenger, a UK-based French designer called Hiba, travels regularly between London and Paris for work and to see family, but says she is thinking of moving back to France. Its been fine, but now there are these silly questions, Im wondering if its all going to be complicated.

Etienne Koehler, a frequent traveller who works for Banque de France, has already relocated back to Paris after 10 years in London. Better get ahead of the mood, I thought there is already less opportunity in the UK. He thinks without doubt there will be fewer travellers between the cities in future, although hes enamoured of the new lounge. Sometimes its nice to be chouchout [pampered].

Jonathan Warburton, a London-based banker for a French bank, who takes the Eurostar every other week, thinks Brexit wont affect his travel unduly. The bank might shift about 5% of its staff over, but Londons the hub, and where the talent is.

News of a new Paris lounge is a bonus, he says: the old one has been a bit of a bunfight these strange swivel chairs facing each other. Mainly though, Warburton values the trains convenience. For all that its occasional disruptions make headlines, he says delays are far shorter and rarer than when he flies. He is not alone: the number of London to Paris flights is in decline, even at the financial districts neighbouring airport, London City.

Petrovic, meanwhile, points to growing ties between France and Britain in the energy, tech and fashion sectors as reasons to be confident. Even Blanc, who admits to a moment of deep pain when he heard the Brexit vote, vows: Regardless, well carry on.

Stephen Crabb urges Theresa May to rework the system as there is nothing to suggest a reduction of migrants is achievable or desirable

People who backed Brexit in the belief it would lead to a cut in immigration into the UK were voting for something that is in effect impossible, a former member of David Camerons cabinet has said.

Stephen Crabb, a former work and pension secretary, said that Theresa May urgently needed to outline a new set of values for a post-Brexit immigration system, or the public may face a rude awakening.

For many, a vote for Brexit was indeed a vote to take back control and return to Westminster the full tools to cut immigration, Crabb said in a article for the Guardian.

The problem is that, set against the popular expectation that Brexit means cutting immigration, there is nothing on the horizon to suggest that achieving any significant reduction is achievable or even desirable.

Crabb argued the fallout from US president Donald Trumps toxic immigration decree had increased the need for a clearer definition of British values towards immigration.

Crabb also joined a number of other Tory MPs on both sides of the Brexit debate who are calling for the UK to guarantee the rights of EU nationals an issue that could be the subject of a House of Commons rebellion during the passage of the Brexit bill next week.

By recognising their value to our economy and society, and the sheer inhumanity and impracticality of ever thinking that these families and individuals could be required to leave the place they call home, we can take the issue off the table altogether. Now that would be a powerful and positive statement of our Brexit values, he said.

He said the economy is continuing to absorb new labour arriving in the UK and no minister has been able to point to any group of foreign workers who should or would not be in the country after Brexit.

On top of that, the governments of Australia, New Zealand, Canada and India have already indicated that they will be looking for easier access for their workers to come to the UK as part of any deal, Crabb added.

There could be another rude awakening for the public when they realise that Brexit will not mean a cut in immigration after all, he said. It would be far better for the government to be upfront with the British public now and begin explaining current labour market and demographic realities. The previous pledge to cut immigration to the tens of thousands is, in truth, increasingly irrelevant.

He suggested the UK should take a more sophisticated approach than a net migration target, perhaps starting with taking overseas students out of the numbers.

May has been clear that cutting immigration is a priority for the government that will require the UK to abandon free movement rules within the EU and leave the single market.

The prime minister has stuck to Camerons target of reducing net migration to the tens of thousands but has not put a timeframe on when this will happen.

Theresa May warned European leaders that the UK is prepared to crash out of the EU if she cannot negotiate a reasonable exit deal in a speech where her tough talking rhetoric prompted key figures in Brussels to say that the country was on track for a hard Brexit.

The prime minister told EU counterparts that any attempt to inflict a punitive outcome on the UK would be an act of calamitous self-harm because it would then slash taxes to attract companies from across the world, in a one-hour address intended to spell out the countrys negotiating strategy.

Although May said that the UK could be the EUs best friend if the article 50 divorce talks went well, she also said she was prepared to walk away. And while I am confident that this scenario need never arise while I am sure a positive agreement can be reached I am equally clear that no deal for Britain is better than a bad deal for Britain, she said.

Eurosceptic ministers and backbenchers were quick to praise May, but her remarks also triggered a backlash from lead European parliament negotiator on Brexit, Guy Verhofstadt. Britain has chosen a hard Brexit. Mays clarity is welcome but the days of UK cherry-picking and Europe a la cart [sic] are over, he said.

Verhofstadt also delivered a tough response to Mays point about business on his Twitter account. Threatening to turn the UK into a deregulated tax heaven will not only hurt British people it is a counterproductive negotiating tactic, he said, urging May to consider the concerns of 48% who voted remain.

Speaking at Lancaster House, London, the prime minister also committed to give both houses of parliament a vote on the final Brexit deal prompting the pound to soar although Downing Street was clear that the alternative to a negotiated exit would be defaulting onto the higher tariffs of World Trade Organisation rules.

No longer be under the jurisdiction of the European court of justice, because we will not have truly left the European Union if we are not in control of our own laws

Explicitly rule out membership of the EUs single market because that is incompatible with migration controls

Not stay in the customs union, but try to strike a separate deal as an associate member to make trading as frictionless as possible

Not be required to contribute huge sums to the EU budget but simply pay towards specific programmes

But would seek a new, comprehensive, bold and ambitious free trade agreement with the EU, and build trading relationships with countries beyond Europe as part of a global Britain strategy

Prominent Brexit supporters said the speech represented a clean break from the EU. Boris Johnson, the foreign secretary, who led the Leave campaign, praised a fantastic speech on Facebook. He has been keen for the prime minister to make a clean break with the EU, rather than seeking to remain inside the single market.

The former Ukip leader Nigel Farage said: I can hardly believe that the PM is now using the phrases and words that Ive been mocked for using for years. Real progress.

However, remain supporters in the Conservative party insisted the plan for Britains future economic relationship with the EU amounted to single market lite. Anna Soubry, who is a key remain supporter, welcomed the language and tone of the speech.

What I am agitated about is that I believe that immigration benefits British business and I think we are making a serious and grave mistake by thinking we can cut the number of migrant workers without damaging our economy, she added.

This position was echoed by Labours Brexit secretary, Keir Starmer, who argued that May was right to attempt to replicate the attributes of the single market in a trade deal.

Starmer said May had committed to something that would mimic full membership. The ball is in her court to deliver. We will hold her to that, he said. However, he and Labour leader Jeremy Corbyn were deeply critical of the threat to slash taxes, which Corbyn said would turn Britain into a bargain basement tax haven on the shores of Europe.

The prime minister said she also wanted to secure the rights of the 3 million-plus EU citizens who live in the UK, suggesting that one or two countries, thought to include Germany, had refused to negotiate an early agreement over the issue.

May said she would accept a phased process of implementation of the Brexit agreement after 2019 but not an unlimited transitional deal that could plunge Britain into permanent political purgatory.

She also called on leave and remain campaigners to put the divisions of the hard-fought referendum behind them. The victors have the responsibility to act magnanimously. The losers have the responsibility to respect the legitimacy of the outcome, she said, claiming that business, MPs and the public wanted to get on with it.

Calling for unity in the UK, May said: Because this is not a game or a time for opposition for oppositions sake. It is a crucial and sensitive negotiation that will define the interests and the success of our country for many years to come. And it is vital that we maintain our discipline.

The prime minister attempted to strike a conciliatory tone with the EU by promising to be a best friend to the bloc after Brexit. But she also claimed the EU had been too unbending in respecting the needs of a diverse set of nations, and too inflexible for British voters. She urged European leaders to learn from Brexit by not tightening a vice-like grip that ends up crushing into tiny pieces the very things you want to protect.

After delivering her speech, May spoke to Jean-Claude Juncker and Donald Tusk, the presidents of the European commission and council, as well as to the German chancellor, Angela Merkel, and French president, Francois Hollande. A Downing Street spokesperson said she had told them that she understood Britain could not remain in the single market but wanted a deal in everyones interests, and said they had welcomed clarity and that Tusk was looking forward to negotiating in a spirit of goodwill.

Tusk also said it marked the start of a sad process but said that at least May was now being realistic.

Other European figures who reacted to the speech included the Czech Europe minister, Tom Prouza, who tweeted: UKs plan seems a bit ambitious. Trade as free as possible, full control on immigration… where is the give for all the take?

The Italian newspaper, La Repubblica, added that Britain was not just leaving the EU but also the common market and everything. It appears that Theresa Mays intention through negotiations with the EU at the end of March is a hard Brexit a very hard Brexit indeed.

One of the biggest challenges for May will be the Irish question. A statement from the Irish government welcomed Mays commitment to retain close relations with the EU, saying it was an ambition they shared. It said it was ready to intensify engagement with other EU countries, adding: Ireland will negotiate from a position of strength, as one of the 27 member states firmly in, and committed to, the European Union.

Sterling was up nearly 3% to around 1.238 US dollars following Mays speech. It also rose 2% against the euro at 1.158.

Some Labour backbenchers were despairing about their partys response, urging their leadership not to throw in the towel and give up on the prospect of membership of a hugely important economic market.

The former shadow chancellor, Chris Leslie, said Labour couldnt provide May with an alibi for her hard Brexit plan.

We should be trying to salvage membership of the single market but to throw in the towel and not even try to stay a member of the single market is sacrificing Britains economic future, he said, arguing that some EU countries might accept reforms towards managed migration.

Italy, Greece, Germany might think about amending that fourth pillar and not to even attempt to ask them is waving the white flag. This is a massively important market we need a bit of fight.

He is planning to lay down an amendment calling for a better deal if the government is forced by the Supreme court to publish an act of parliament before triggering article 50.

Tim Farron, the Lib Dem leader, said it was wrong that there would be no referendum on the final deal. The people voted for departure, they should be given a vote on the destination. This is a theft of democracy.

Downing Street sources said the prime minister had discussed the speech with both the leaders of the Scottish and Welsh administrations on Tuesday morning. But despite these conversations, May received an immediate rebuke from Nicola Sturgeon who warned the plan could be economically catastrophic.

Claiming that May was being driven by the obsessions of the hard right of the Tory party, Sturgeon argued that her demands for a special deal for Scotland were not being listened to.